1. Field of the Invention
This invention relates to a firetube heater for use in fired heaters including boilers and vapor generators, which provides a large heat output in a relatively short, small-diameter tube. More particularly, this invention relates to a firetube heat exchanger suitable for use in such fired heaters having corrugated internal fins for promoting the transfer of heat from the products of combustion disposed within the firetube through the firetube walls and into the medium to be heated.
2. Description of Prior Art
Internally finned heat exchanger tubes are known in the art. See, for example, U.S. Pat. No. 4,554,969 which teaches a coaxial finned tube heat exchanger. U.S. Pat. No. 4,163,474 teaches an internally finned tube heat exchanger having fins in the form of a series of elongated V-shaped strips, formed in accordance with one embodiment by a corrugated metal. The fins are provided with holes to permit transverse flow of fluid through each fin as the fluid also travels longitudinally along the tube. One problem with this design, particularly when used with a high temperature heat exchange fluid, such as products of combustion, is the tendency of the fins to overheat at the point where the fluid is introduced into the tube beneath the fins. This is due to the very high heat transfer coefficient present at the leading edges of the fins, the point at which the fluid is introduced beneath the fins.